1. Field of the Invention
The invention relates to a microprocessor-based control system for a scissor type aerial work platform. More particularly, the invention relates to the use of a microprocessor-based control system for a scissor type aerial work platform which allows a reduction in the number of components required in the control function. The invention also relates to a multiplexing device which reduces the number of conductors required in the control system.
2. Description of the Related Art
Work Platforms are utilized for a variety of different uses, such as: a) loading and unloading of items in a warehouse, and b) repairing components located at a particular elevation, such as repairing a broken ceiling light in a gymnasium. FIG. 1a shows a conventional work platform which can be used at a warehouse, for example. The work platform, which in this case is shown as a scissor type aerial work platform 10, can be used to move large boxes from one location to another, or it can be used to move a worker to a particular location as the work platform 10 is raised or lowered to a particular height. The work platform 10 includes a base portion 20 and a vertically movable platform portion 30 (also called "aerial work platform").
One important aspect of aerial work platforms is the control of the movement of the movable platform 30 with respect to the base portion 20. Typically, this is done by monitoring inputs made by an operator, and by raising or lowering the movable platform 30, extending or retracting a deck on the movable platform 30, or driving the work platform 10 based on the particular operator input. FIG. 1b shows the same work platform 10 as in FIG. 1a, but with a deck 40 extended on the movable platform 30, thereby allowing an operator on the movable platform 30 greater range of movement.
U.S. Pat. No. 5,274,331, to Littlejohn et al., shows a system in which network communication concepts are applied to a motor and/or motion control system. Specifically, a wheelchair control is shown in the Littlejohn et al. reference, in which three modules are interconnected by an RS-485 bus. The modules are: a) a user command module, b) a motherboard controller module, and c) a drive motor controller module. In the Littlejohn et al. system, commands entered at the command module are transmitted to the motherboard controller through the bus. The motherboard controller communicates with the motor controller through the bus.
U.S. Pat. No. 4,519,042, to Minamida et al., shows a method for checking the operation of a combinatorial weight measuring apparatus to determine whether weighing machines and a microcomputer which determines the optimum combination of objects are operating properly. Also shown in Minamida's system is a multiplexer which is used for communicating information from a plurality of controlled elements, i.e., weighing machines, to a microcomputer.
U.S. Pat. No. 4,691,805, to Kiski, shows a lifting apparatus in which a number of functions are controlled by software. These functions include the extension of a stretchable boom, inclination of the stretchable boom, and the orientation of a work platform at the end of the boom.
U.S. Pat. No. 5,011,358, to Andersen et al., shows a controller for a forklift, which compares programmed store and retrieve heights for various shelves in a warehouse with the current height of the fork. The Andersen et al. system also displays to the operator an indication when the fork is at or within a predetermined range of the store or retrieve height of the shelf.
None of the above systems show a device which can accommodate both analog and digital inputs to control an aerial type work platform in an expedient manner, nor do they show a device that can receive various sensor inputs as well as platform and ground select inputs to control a plurality of valves to actuate a particular work platform function.
Further, each of the above-mentioned systems uses external relays and diodes to provide the needed control of the work platform. The various control devices are not centrally located, and do not use solid-state components for the control function of the work platform.